Creating Abundant Open Metal Sites in MOFs by Dual-Coordination Design for Enhanced Electrocatalytic Activity.

Metal-organic frameworks (MOFs) with well-defined crystalline structures offer ideal platforms to unravel structure-property relationships, but their low density of accessible metal sites limits catalytic activation. Efforts to generate open metal sites often compromise structural integrity, obstructing mechanistic investigation. In this study, we convert single-coordinated MOFs into dual-coordinated frameworks, enabling controlled creation of unsaturated metal sites to boost electrocatalytic performance while preserving crystal framework for structure-property study. As a proof-of-concept, we transform Zn─N single-coordinated ZIF-L into Zn─N/O dual-coordinated MOFs (B-MOFs), where strong Zn─N bonds act as structural pillars and weaker Zn─O bonds serve as removable linkers. Upon annealing at 500 °C, selective cleavage of Zn─O bonds produces defective MOFs (dB-MOFs) with abundant open Zn sites and a well-retained crystal structure. The dB-MOF grown on carbon cloth (CC) exhibits high performance in hydrazine oxidation reaction (HzOR), significantly superior to pristine B-MOF/CC. A combination of material characterizations and theoretical calculation demonstrates that the removal of Zn─O bond creates abundant electron-deficient Zn sites, which enhance the adsorption of HzOR intermediates and lower the reaction energy barriers.